Command-line arguments in the C language
The C language provides a method to pass parameters to the main() function. This is typically accomplished by specifying arguments on the operating system command line (console).
The prototype for main() looks like:
int main(int argc, char *argv[])
{
…
}
There are two parameters passed to main(). The first parameter is the number of items on the command line (int argc). Each argument on the command line is separated by one or more spaces, and the operating system places each argument directly into its own null-terminated string. The second parameter passed to main() is an array of pointers to the character strings containing each argument (char *argv[]).
For example, at the command prompt:
test_prog 1 apple orange 4096.0
There are 5 items on the command line, so the operating system will set argc=5 . The parameter argv is a pointer to an array of pointers to strings of characters, such that:
argv[0] is a pointer to the string “test_prog”
argv[1] is a pointer to the string “1”
argv[2] is a pointer to the string “apple”
argv[3] is a pointer to the string “orange”
and argv[4] is a pointer to the string “4096.0”
Notes
• The main() routine can check argc to see how many arguments the user specified.
• The minimum count for argc is 1: the command line just contained the name of the invoked program with no arguments.
• The program can find out its own name as it was invoked: it is stored in the argv[0] string! Some operating systems don't provide this feature, however.
• The arguments from the command line are not automatically converted: the characters are just copied into the argv strings.
• If an argument on the command line is to be interpreted as a numerical constant, such as argv[1] and argv[4] in this example, it can be converted using a string conversion.
int int_val; float float_val;
sscanf(argv[1],”%d”,&int_val);
sscanf(argv[4],”%f”,&float_val); and
printf(“The 3rd and 4th items on the command line are %s and %s\n”, argv[2], argv[3]);
results in: The 3rd and 4th items on the command line are apple and orange
The string functions atoi(), atol(), atof(), etc., will also work.
